Simple design of an in situ generated iron sulfide/carbon heterostructure with N, S codoping for high performance lithium/sodium-ion batteries

Abstract The development of low-cost, high-energy-density batteries with high capacity and long-term cyclability is inevitable to meet the recurring energy demand. Here, we report a feasible and straightforward design of heterostructured electrode; in situ generated iron sulfide nanoparticles enclosed in a multifunctional carbon nanostructure with N, S codoping (FeS@NS-CR) for efficient lithium and sodium-ion storage. The in situ generation of nanosized FeS particles in a rationally designed carbon sheath with heteroatom doping mitigates the sluggish kinetics inherent in FeS, offers sufficient buffering to accommodate the volume changes during cycling, and facilitates the fast diffusion of alkali ions. The heteroatom functionalized carbon matrix also offers physical and chemical entrapment of polysulfide species during cycling, leading to stable cycle performances in LIBs and SIBs. Unlike previous works on FeS with low active material content, the FeS@NS-CR composite with 82% active FeS can deliver an excellent capacity of ∼500 mAh g-1 (vs. Li/Li+)) and 432.7 mAh g-1 (vs. Na/Na+) after 500 cycles at 1000 mA g-1 without compromising energy density. The FeS@NS-CR composite also shows high reversible capacities of 525.8 mAh g-1 at 8000 mA g-1 (vs. Li/Li+) and 409.3 mAh g-1 at 5000 mA g-1 (vs. Na/Na+), demonstrating excellent rate capability.